This invention relates to a method for controlling the crystal morphology of silicon nitride. More particularly, it relates to a method for controlling the crystal morphology of silicon nitride by controlling the bulk density of the intermediate product formed by reacting a chlorosilane with ammonia, with an increase in bulk density over about 0.1 g/cc resulting in at least a portion of the silicon nitride having equiaxed crystals.
Cross reference to copending application.
This invention is related to copending application Ser. No. 768,995 entitled "Production of Silicon Nitride," filed Aug. 26, 1985 and assigned to the same assignee as the present application. Application Ser. No. 768,995 relates to a method for producing silicon nitride by reacting a chlorosilane with a controlled amount of ammonia to produce an intermediate chloroimide reaction product which has a relatively low ammonium chloride content.
Silicon nitride has found use in a wide variety of applications such as wear parts, milling media, and heat engine components.
In certain applications such as slip casting and in composites it is desirable to have silicon nitride of fibrous crystal structure.
In certain applications such as dry pressing, isopressing, extrusion, and injection molding it is desirable to have silicon nitride of equiaxial crystal structure.
U.S. Pat. No. 4,387,079 describes controlling the crystal structure of silicon nitride by adjusting the calcination temperature in formation of the silicon nitride.
Japanese Pat. No. 0073412 discloses a process for synthesizing silicon nitride by reacting a silicon halide, such as silicon tetrachloride, with ammonia at 600.degree.-1500.degree. C. in a gas containing ammonia and subsequently heating in an inert gas. This reference does not teach controlling the bulk density of an intermediate to control the crystal morphology of the silicon nitride product.